Noninvasive temperature-measuring techniques

Acoustic chemometrics has its greatest benefits in cases where haditional sensors and measurement techniques, such as flow, temperature and pressure transmitters cannot be used. In many processes it is preferable to use noninvasive sensors because invasive sensors may cause disturbances, for example fouling and clogging inside the process equipment such as pipelines, reactors cyclones, etc. In this chapter we concentrate mainly on new industrial applications for acoustic chemomehics, and only discuss the necessary elements of the more technical aspects of the enabling technology below - details can be found in the extensive background literature [3-5],... 

Measurement techniques for the resolution of concentration and temperature profiles in chemical reactors with heterogeneously catalyzed gas-phase reactions are a very useful tool not only for a better understanding of the reaction sequence and derivation of reaction kinetics but also for the elucidation of the coupling between catalytic reaction kinetics and mass and heat transport. The combination of numerical simulations of the reactive flow in catalytic reactors incorporating microkinetic reaction schemes and those recently developed invasive and noninvasive in situ techniques can today support the optimization of reactor design and operating conditions in industrial applications. 

Combination of Eqs. (62) and (63) or (66) allows the estimation of the polymerization rate from temperature measurements. This method, which is called reaction calorimetry (see Section 6.10.1.6), is a powerful noninvasive on-line monitoring technique and it has been extensively apphed to polymerization reactors [113,114]. 

The objective ia any analytical procedure is to determine the composition of the sample (speciation) and the amounts of different species present (quantification). Spectroscopic techniques can both identify and quantify ia a single measurement. A wide range of compounds can be detected with high specificity, even ia multicomponent mixtures. Many spectroscopic methods are noninvasive, involving no sample collection, pretreatment, or contamination (see Nondestructive evaluation). Because only optical access to the sample is needed, instmments can be remotely situated for environmental and process monitoring (see Analytical METHODS Process control). Spectroscopy provides rapid real-time results, and is easily adaptable to continuous long-term monitoring. Spectra also carry information on sample conditions such as temperature and pressure. 

Radiometry. Radiometry is the measurement of radiant electromagnetic energy (17,18,134), considered herein to be the direct detection and spectroscopic analysis of ambient thermal emission, as distinguished from techniques in which the sample is actively probed. At any temperature above absolute zero, some molecules are in thermally populated excited levels, and transitions from these to the ground state radiate energy at characteristic frequencies. Erom Wien s displacement law, T = 2898 //m-K, the emission maximum at 300 K is near 10 fim in the mid-ir. This radiation occurs at just the energies of molecular rovibrational transitions, so thermal emission carries much the same information as an ir absorption spectmm. Detection of the emissions of remote thermal sources is the ultimate passive and noninvasive technique, requiring not even an optical probe of the sampled volume. 

Milne et al. [154] have developed stereotactically guided laser thermotherapy for breast cancer in situ measurements. They determine the temperature field within the breast to highlight potential tumors. A review paper by Tromberg et al. [155] discusses the noninvasive in vivo characterization of breast cancer tumors using photon migration spectroscopy. They compare the use of this technique with straightforward NIR spectroscopy. 

It is essential to provide accurate measurements of intratissue temperature distributions during normothermia and hyperthermia. New developments in the noninvasive thermometric techniques using MRI and microwave should alleviate some of these problems. 

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